It is known that nematic liquid crystals show various electro-optical effects due to their dielectrical anisotropy in electrical fields (G. Meier, J. G. Grabmaier, Application of Liquid Crystals, Berlin-Heidelberg-New York, Springer Verlag 1975). Modulation of light may be obtained in appropriate cells by aid of these effects as well as a display of numbers, symbols and images.
Nematic liquid crystals with negative dielectrical anisotropy show the dynamic dispersive effect which allows the construction of electro-optical elements without the use of polarizers. In nematic liquid crystals with positive dielectrical anisotropy, the Schadt-Helfrich effect occurs, which is based upon the deformation of artifically distorted nematic layers in electrical fields. This arrangement needs two polarizing filters.
Presently, no pure compound nor a mixture of a plurality of substances is known which could fulfill all demands which are required from a substance for electro-optical elements, particularly low melting temperatures and high temperatures of transparency. The properties of mixtures may be improved because the melting point of eutectic mixtures diminish with the number of components. The temperatures of transparency of mixtures may be raised considerably by the addition of substances with high temperatures of transparency.